Production of brown cobaltous oxide and cobalt salts



DE WITT H. wEsTYETAL 2,909,408

Filed Dec. 14, 1956 PRODUCTION OF BROWN COBALTOUS OXIDE AND COBALT SALTS Oct. 20, 1959 l described hereinabove.

United States Patent C PRODUCTION OF BROWNl COBALTOUS OXID AND COBALT SALTS De Witt H. West, Port Eynon, Swansea, and Stanley C. Townshend and David M. Llewelyn, Clydach, Swausea, Wales, assignors to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Application December 14, 1956, Serial N o. 628,278

Claims priority, application Great Britain January 23, 1956 7 Claims. (Cl. 23-183) 'Ihe present invention relates to cobalt compounds and more particularly to a vhighly reactive oxide of cobalt which is extremely soluble in both inorganic and organic acids, to a method of preparing the same and a method for producing cobalt salts therefrom.

As will be readily appreciated by those skilled in the v art, in the refining of cobalt it is generally necessary to separate it from nickel with which it commonly occurs. This is usually done by selective precipitation from solution of the cobalt as cobaltic hydroxide Co(OH)3, which, after being washed and roasted, is marketed as black cobaltosic oxide C0304. -This oxide cannot be directly used for the manufacture of cobalt salts since it is almost or substantially insoluble in the common acids, except hydrochloric acid in which it dissolves 'with the evolution of poisonous chlorine fumes.

Heretofore, it has been customary in the art to produce cobalt salts by the direct reduction of the cobaltosic oxide to metallic cobalt and then reacting the latter with acid. Direct reduction of cobaltosic .oxide to metallic cobalt, however, leaves the cobalt in the Aform of finely divided metal powder which, although soluble in inorganic acids, is substantially insoluble in most organic acids and is extremely sensitive to oxidation, so that great care is necessary in handling the powder after reduction. If the cobaltosic oxide is made into pellets with a carbonaceous material, eg., llour, and 4the pellets are heated to, say, 800 C., massive cobalt is formed and, on cooling, is stable in air. However, the rate of dissolution of this massive cobalt is much slower than that of the powder, many hours being required before dissolution is complete.

Attempts have also been directed to employing co- ,balt hydrate in the commercial preparation of cobalt salts since cobalt hydrate is relatively soluble in acids. It has been found that while cobalt hydrate may be soluble in acids the utilization thereof in preparing cobalt salts is disadvantageous since it is extremely diicult to handle commercially, thus giving rise to divers ditiiculties. Endeavors made to avoid the formation of a hydrate phase have resulted in processes requiring extremely long periods of time to form the cobalt salts. v Thus, there has long existed in the art a dire need for a satisfactory commercial procedure for easily and readily producing cobalt salts while avoiding or obviating the difficulties overcome the foregoing diiculties and other difficulties, none, as far as we are aware, was entirely successful when carried into practice commercially on an industrial scale.

It has now been discovered that cobalt salts of both inorganic and organic acids can be easily and economically provided on a commercial scale using a special highly reactive oxide of cobalt prepared by a special process involving the selective reduction of cobaltosic oxide to brown cobaltous oxide. The present inventionV is based on the discovery that brown cobaltous oxide produced by Although attempts were made to A 2,909,408 Patented Oct. 20, 1959 ice It is an object of the present invention to` provide a process for the commercial production of cobalt salts of both inorganic and organic acids.

Another object of the invention is to provide a specially prepared brown cobaltous oxide extremely soluble in both inorganic and organic acids, including weak acids used in the manufacture of paint driers, e.g., naphthenic acid.

The invention also contemplates providing a specially prepared brown cobaltous oxide which is both more stable than cobalt powder and very soluble not only in inorganic acids but also organic acids.

It is a further object of the invention to provide acommercial process for the preparation of a highly soluble brown cobaltous oxide. Y I

The invention further contemplates providing a highly satisfactory commercial and easily controllable process for the production of cobaltous salts in relatively short periods of time. t

It is another object of the invention to provide a commercial method for producing cobalt salts using a special ly prepared brown cobaltous oxide.

Other objects and advantages will become apparent from the `following description taken in conjunction with the accompanying drawing 'which sets forth a graph depicting, in accordance with the present invention, the inter-relationship existing between temperature of reduction and the ratio of the oxidizing to reducing constituents of gas mixture employed.` v

Generally speaking, `the present invention contemplates' the provision of a specially-prepared brown cobaltous oxide characterized by a high reactivity, including a high degree of solubility in acids. This highly soluble brown oxide. It is preferred to work Within the range of 350 C. to 450 C. and most advantageously at 400 C. Moreover, it is preferred in accordance with the invention that the oxidizing component of the gas mixture be selected from the group consisting of steam, carbon dioxide or aj mixture thereof and the reducing componentbe selected from the group consisting of hydrogen, carbon monoxide or a mixture thereof. Cobalt salts or soaps are prepared by reaction between the cobaltous oxide thus produced and an acid, with or without further reaction of the initial reaction products.

In carrying thepresent invention into practice, it is important that the temperature at which the selective duction is performed under contemplated reducing'con-' ditions be maintained over a range of about 300 C.' to

about 500 C. asindicated by the accompanying graph. We have found that at temperatures below about 300 C. the reduction step proceeds too slowly and thatas rthe temperature is raised above about 500 C. the reactivity.

of theA cobaltous oxide with acids, particularly `weak organic acids, decreases progressively with increasing temperature. Furthermore, it is important that the. cobaltosic oxide not be reduced to metallic cobalt. Bel low the shaded area on the graph, cobaltosieoxide is re-V duced to metallic cobalt; above the shaded area, reduction to cobaltous oxide is not complete. Thus, if reducing conditions outside the shaded area of the graph are used, the desired production of brown cobaltous oxide is not achieved. The gas mixture can vary widely in composition but for optimum results must be progressively weaker in reducing components the higher the temperature, i.e., it has been found that the ratio of oxidizing gas to reducing gas should preferably be increased as the temperature is progressively increased. The gas ratios expressed on the graph are volume ratios.

The reduction of the cobaltosic oxide should be continued until all or substantially all of it has been converted into brown cobaltous oxide, but substantially none has been reduced to the metallic state. Heating of the cobaltosic oxide for about 1 hour at 400 C. is equivalent to 2 hours at 350 C. and 3%: hour at 450 C., respectively'. We prefer to select the reduction conditions so that reduction is complete in between 1 and 2 hours and, to this end, it is a preferred feature of our invention to heat the cobaltosic oxide as an unagglomerated powder, the particle size of which is not greater than about one micron in diameter. The speed of reduction is dependent on the particle size of the cobaltosic oxide; the finer the cobaltosic oxide powder, the more rapid is the reduction and also the more soluble is the brown cobaltous oxide produced.

For the purpose of giving those skilled in the art a better understanding and a better appreciation of the advantages of the invention, the following illustrative examples are given:

Example 1 One hundred grams of fine, black cobaltosic oxide C0304` (73.4% Co) were put in a boat 6 inches long and inch deep. The boat was heated to 400 C. and a mixture, by volume, of six parts of steam and one part of hydrogen was passed thereover for one hour. After rapidly cooling the boat in an atmosphere of dry carbon dioxide, it was found that 99.5% of the product so produced (containing 77.5% cobalt) dissolved in an equivalent amount of dilute sulphuric acid in one hour at 90 C.

Considering the gas mixture of steam and hydrogen, the amount of cobaltous oxide produced increases as the volume ratio of steam to hydrogen decreases, but there must be much more steam than hydrogen if the production of metallic cobalt is to be avoided. This is clearly shown by results obtained for l hours heating with a reduction temperature of 400 C. as given below, the solubility of the product in dilute sulphuric acid being a measure of the amount of cobaltous oxide present:

Ratio of Point; on Graph Steam/H2 Percent solubility of Product some cobalt metal produced.

Example II Using a mixture of steam and water gas, the process wasV carried out in the same manner as described in connection with Example I. The water gas contained 51% hydrogen, 38% carbon 'monoxide and 3.6% carbon dioxide, the volume ratioof steam to water gas being 4: 1. The reduction resulted in a product of which 97% was soluble in dilute sulphuric acid, and Was'brown cobal-l tous oxide. When a mixture of steam and. Water gas is .4 used, the ratio of steam to water gas will, of course, depend on the composition of the water gas. At 400 C. and with a water gas composition as described hereinabove, it is preferred to use the foregoing ratio of steam to water gas of about 4:1, i.e., a'ratio of oxidizing to reducing components of about 4.5 :1 (point G on the graph).

Example Ill In another example carried out in the same way as described in connection with Example I, a gas mixture of steam and producer gas was employed. The producer gas contained 25.6% carbon monoxide, 17.2% hydrogen and 6.8% carbon dioxide, the ratio of steam to producer gas being about 2:1, i.e., the ratio of oxidizing components to reducing components being about 4.8:1 (point H on the graph). The reduction provided a product which was 99% soluble in an equivalent amount of dilute sulphuric acid, and was brown cobaltous oxide. As in the case of steam and water gas, the ratio of steam to producer gas depends on the composition of the latter. Using a mixture of steam and producer gas, the preferred conditions vary between a ratio of oxidizing to reducing components of from 3.4:1 at 350 C. (point I on the graph) through the point H to a ratio of about 8:1 at 450 C. (point K .on the graph).

Example IV A further embodiment was conducted to illustrate the results achieved using a gas mixture of carbon dioxide and carbon monoxide. The example was otherwise conducted in the manner described in connection with Example I and it was determined that the reduction resulted in a product of which 95% was soluble in an equivalent amount of dilute sulphuric acid and was brown cobaltous oxide. A preferred ratio of carbon dioxide to carbon monoxide of 4:1 was used in this embodiment (point I on the graph).

In the examples given above, some of the dissolution of the brown cobaltous oxide in the dilute sulphuric acid took lplace in the markedly short period of 5 minutes.

The cobaltosic oxide to be selectively reduced can be passed continuously through a furnace and the cobaltous oxide so formed can then be quenched in water. Advantageously, the oxide can be fed into trays which gradually travel through an indirectly heated tunnel furnace, with the furnace atmosphere being preferably a mixture of steam and producer gas. Just before the trays leave the furnace, they may be tipped to discharge the cobaltous monoxide on to a short length of conveyor leading to a water quenching tank. The wet mass of oxide can be transferred directly from this tank to, for example,l

vats containing hot sulphuric acid. After all the acid has reacted with the oxide, the liquor can be ltered and any undissolved oxide returned to the tunnel furnace and there be mixed with fresh cobaltosic oxide.

The cobaltous oxide used in this invention and prepared as described herein should not be allowed to reoxidize and it is preferably either quenched in water or rapidly cooled in an inert ory weakly reducing atmosphere. When cold, the oxide may be discharged into the air. However, as it gradually acquires a surface film of black oxide if it is exposed to air and this film lowers the solubility in sulphuric acid, it should be stored in a sealed container under dry inert gas unless it is to be used immediately.

'I'he cobaltous oxide prepared in accordance with this invention will dissolve rapidly and practically completely not only in sulphuric acid, but also in the usual inorganic acids, e.g., hydrochloric acid, nitric acid and phosphoric acid, to form the corresponding cobaltous salt. Its rate of solution is much faster than that of cobalt metal even in powder form since the rate of the latter is controlled by the evolution of hydrogen, whereas no gas is evolved with the cobaltous monoxide prepared according to the invention,

Similarly, the cobaltous oxide is readily soluble in such organic acids as acetic acid, citric acid, oxalic acid and formic acid to form the corresponding organic salts. Thus, when the oxide was heated in an equivalent amount of acetic acid at 90 C., 90% dissolved in-S minutes and this figure increased to 97.5% in one hour. Similarly, when the oxide was treated at 50 C. in a 10% formic acid solution, 91% dissolved in two hours.

The cobaltous oxide of the present invention is also very soluble in such weak organic acids as naphthenic acid. Naphthenic acid, which has an acid value of 228,

is used in the manufacture of metal soaps and paint driers, as are 2 ethyl-hexoic acid, which has an acid value of 380, and tall oil, which is a mixture of acids and has an acid value of 183. The oxide made according to the invention may advantageously be used in the manufacture vof soaps from any of these substances. Thus, the oxide will dissolve completely in naphthenic acid in a few minutes at 160 C. to form cobalt napthenate.

If desired or necessary, the original reaction product prepared by the reaction between cobaltous oxide and an acid may undergo further reaction to form a salt or soap. For example, cobalt naphthenate can be prepared by the following reactions:

CoSO4-l-sodium naphthenate=coba1t naphthenate-l-HzSO.,z

It is most surprising that the brown cobaltous oxide prepared according to the invention will dissolve so rapidly in acids because the monoxide produced by the thermal decomposition of cobaltosic oxide according to the equation 2Co304 6CoO-i-O2 is not so reactive and cannot conveniently be used for the manufacture of cobalt salts and soaps. Moreover, the temperatures used in accordance with our invention are low in comparison with that required to decompose the cobaltosic oxide by heat, e.g., 900 C., to produce cobaltous oxide. Thus, it is to be noted that the present invention is not to be confused with such oxides and processes for producing the same.

As is well known, the production of cobalt compounds including cobalt salts nds a wide and diversied application in sundry important industrial and commercial elds. The present invention is particularly applicable in the manufacture of paints, varnish driers, soaps, ceramics, pigments, synthetic inks and other applications. Y

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications land variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. A process for producing a brown cobaltous oxide which is characterized by a. high degree of solubility in both inorganic and organic acids which comprises selec- 6 tively reducing cobaltosic oxide by heating it at a teniperature between 300 C. and 500 C. in a gaseous mixture comprised of oxidizing and reducing components,

said oxidizing component being selected from the group consisting of steam, carbon dioxide and mixtures thereof and said reducing component being selected from the group consisting of hydrogen, carbon monoxide and mixtures thereof, the ratio of oxidizing component to reducing component and the temperature of selective reduction being correlated to fall within the area XY ZX of the accompanying graph.

2. A process as described in claim 1 wherein the oxidizing component is steam and the reducing component is hydrogen.

3. A process as defined in claim 1 wherein the oxidizing component is steam and the reducing component is a gaseous mixture containing hydrogen and carbon monoxide.

4. A process as defined in claim 1 wherein the oxidizing component is comprised of steam and carbon dioxide and the reducing component 4is comprised of hydrogen and carbon monoxide.

5. A process as defined in claim 1 wherein the oxidizing component is carbon dioxide and the reducing component is carbon monoxide.

6. A process as dened in claim 1 wherein the cobaltosic oxide is an unagglomerated powder, the particles of which are not greater than about one micron in diameter.

7. A process for producing cobalt salts which comprises the steps of selectively reducing cobaltosic oxide to brown cobaltous oxide by heating it at a temperature between 300 C. and 500 C. in a gaseous mixture comprised of oxidizing and reducing components, said oxidizing component being selected from the group consisting of steam, carbon dioxide and mixtures thereof and said reducing component being selected from the group consisting of hydrogen, carbon monoxide'and mixtures References Cited in the file of this patent UNITED STATES PATENTS 1,329,323 Ellis Ian. 27, 1920 2,785,049 Whaley Mar. 12, 1957 FOREIGN PATENTS 15,591 Great Britain 1906 OTHER REFERENCES Thorpes Dictionary of Applied Chemistry, 4th ed., vol. III, page 218.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 14, 1935; Longrnans, Green and Co., N.Y.; pages 558, 561, 564 and 580. 

1. A PROCESS FOR PRODUCING A BROWN COBALTOUS OXIDE WHICH IS CHARACTERIZED BY A HIGH DEGREE OF SOLUBILITY IN BOTH INORGANIC AND ORGANIC ACIDS WHICH COMPRISES SELECTIVELY REDUCING COBALTOSIC OXIDE BY HEATING IT AT A TEMPERATURE BETWEEN 300*C. AND 500*C. IN A GASEOUS MIXTURE COMPRISED OF OXIDIZING AND REDUCING COMPONENTS, SAID OXIDIZING COMPONENT BEING SELECTED FROM THE GROUP CONSISTING OF STEAM, CARBON DIOXIDE AND MIXTURES THEREOF AND SAID REDUCING COMPONENT BEING SELECTED FROM THE GROUP CONSISTING OF HYDROGEN, CARBON MONOXIDE AND MIXTURES THEREOF, THE RATIO OF OXIDIZING COMPONENT TO REDUCING COMPONENT AND THE TEMPERATURE OF SELECTIVE REDUCTION BEING CORRELATED TO FALL WITH THE AREA XYZX OF THE ACCOMPANYING GRAPH. 